1. Field of the Invention
The present invention relates, in general, to pyramid-shaped near field probes using surface plasmon waves and, more particularly, to a near field probe, which forms and changes a near field at the aperture of the probe using a surface plasmon wave propagating through the boundary surface between a probe body made of a dielectric and metal films symmetrically coated on the sides of the probe body.
2. Description of the Related Art
Generally, in order to store a greater amount of information per unit area in an optical information storage device, the wavelength of a recording light source must be reduced or the numerical aperture of a condensing lens must be increased. In the case of wavelength, a blue laser diode may be developed, and in the case of numerical aperture, a maximum of 1.0 may be obtained.
However, such an optical information storage scheme is limited in recording high density information in an advanced information storage device requiring high density recording due to the refractive limit of light, etc.
For alternative technology for overcoming the above limitation, Scanning Probe Recording (SPR) technology using the probe of an Atomic Force Microscope (AFM), super resolution media technology, technology using a near field probe overcoming the refractive limit of light, etc. have been developed. In particular, a near field probe using an optical fiber has been developed.
With reference to FIGS. 1 to 5, the construction and operation of a near field probe using an optical fiber is described.
As shown in FIGS. 1 and 2, an optical fiber 10 used for a near field probe includes a core 11 for guiding externally incident light, and a cladding 12 surrounding the core 11 to protect the core 11.
In this case, the core 11 is made of quartz glass with a diameter of 10 μm and plastic material, and the cladding 12 is made of glass material having a refractive index differing from that of the core 11.
A process of forming a probe on the optical fiber 10 having the above construction is described below.
As shown in FIG. 3, after one end of the core 11, not heated, is firmly held using a mechanism while heat is applied to the other end thereof at a certain temperature or above and the other end is heated, the heated portion is pulled using a mechanism, so that a conical optical fiber 14 having an aperture 13 is formed.
In this case, the aperture 13 is preferably formed to cause the diameter thereof to be about 0.05 to 0.3 μm. If the aperture 13 is formed in this way, the size of a near field formed at the aperture 13 due to the light transmitted through the conical optical fiber 14 is about 100 nm or less.
As described above, after the conical optical fiber 14 is formed through a pulling process, a metal, such as aluminum, is coated to form a metal layer 15 on an external surface of the conical optical fiber 14 as shown in FIG. 4, so that an optical fiber probe 16 using the optical fiber is completely produced.
However, the above-described optical fiber probe 16 using the optical fiber is disadvantageous in that, if a traveling wave 20 propagates into the conical optical fiber 14 and reaches a region near a diameter having a size similar to the wavelength of the traveling wave while propagating into the optical fiber 14, as shown in FIG. 5, the progression of light is difficult, so that the intensity of the traveling wave 20 decreases sharply.
At this time, in order to obtain the information on spatial resolution below the wavelength, the diameter of the aperture 13 of the optical fiber probe 16 must be smaller than the wavelength of the traveling wave 20. Therefore, as the traveling wave 20 approaches the aperture 13, the traveling wave 20 almost disappears, and only an evanescent wave 21, losing traveling characteristics, exists in the region of the aperture 13 of the optical fiber probe 16.
At this time, the intensity of the evanescent wave 21 existing near the aperture 13 of the optical fiber probe 16 decreases to 0.01% or less of the intensity of incident light. For a method of solving the above disadvantage, a metal film functioning to allow light with a size below the refractive limit to pass through the optical fiber 14 as well as to prevent light guided through the conical optical fiber 14 from leaking to the outside is coated on the external surface of the optical fiber 14.
However, since the optical fiber probe using an optical fiber constructed as described above has extremely low transmissivity, it has limitations in Signal-to-Noise (S/N) ratio and recording and reproducing speed, so that the optical fiber probe causes a great number of problems when it is used for a high density optical recording apparatus.
Further, the above-described optical fiber probe using an optical fiber is problematic in that, since light guided to the aperture region is basically formed to have multiple modes, such as traverse magnetic modes TM00, TM10 and TM20, it is difficult to form a sharp beam spot on the aperture.
Further, the optical fiber probe using an optical fiber is problematic in that, since it is manufactured in such a way that, after heat processing is executed for the optical fiber, a conical optical fiber is formed by a pulling operation, and a metal film is coated on the conical optical fiber, it is difficult to structurally manufacture the optical fiber probe.